An essential step of the mitotic process is the attachment of chromosomes to the spindle by kinetochore microtubules. Both attachment and kinetochore micortubule formation are presumed to take place during prometaphase subsequent to the disintegration of nuclear envelope. We have begun an investigation of the processes of attachment and kinetochore microtubule formation through the analysis of crane-fly spermatocytes during the transition from prophase into prometaphase. Results obtained from living prophase cells indicate that chromosomes move inside the prophase nucleus, suggesting that they already may be attached to the movement machinery before the nuclear membrane disintegrates. The prophase chromosomes appear to be located at the periphery of the nucleus, perhaps in association with the nuclear envelope. Additional findings are that prophase movements are sensitive to both cyanide and cold treatment, but they are insensitive to treatment with Colcemid. Whether prophase movements truly are microtubule-independent is being investigated at the ultrastructural level in fixed cells. Emphasis is being put on the relationships among prophase chromosomes, the nuclear envelope and the numerous cytoplasmic microtubules that have been observed in untreated cells adjacent to the nuclear envelope. The location of kinetochores within the prophase nucleus also is being investigated.